Tubular condenser of variable capacity



Get. 17, E967 0. VINZ- 3,348,106 Y TUBULAR CONDENSER OF VARIABLECAPACITY Filed June 15, 1.966

INVENTOR 2 5772071572;

United States Patent 3,348,106 TUBULAR CONDENSER OF VARIABLE CAPACITYOttmar Vinz, Landshut, Germany, assignor to JENAer Glaswerlr Schott dzGem, Mainz, Germany, a corporation of Germany Filed June 15, 1966, Ser.No. 557,792 Claims priority, application Germany, June 16, 1965,

3 Claims. Ci. 317 249 ABSTRACT OF THE DISCLOSURE The invention relatesto a tubular condenser of variable capacity in which a tubular member isprovided on its outer circumference with a stationary electrode which isarranged opposite a slidable electrode arranged in the interior of thetubular member. The slidable electrode has the form of an axiallyadjustable piston which is mounted on an axially adjustable rod whichmay consist of a threaded spindle. Such type of condensers are usedamong other fields also in the UHF range.

Condensers of this type are known which are constructed as ceramic orglass tube trimmer. Furthermore, such condensers have been used in whichthe dielectric comprises an organic material.

These trimmer-type condensers are employed below 100 mHz. principallyfor a fine adjustment of circuits and in this type of use are suitablyarranged in parallel to a condenser having a substantially greatercapacity. In the case of higher frequencies, particularly above 100mHz., these trimmer condensers are used directly for the construction ofelectric circuits, and in that case, they constitute exclusively theoscillatory circuit capacity. Furthermore, these condensers are used forresonance compensation of geometrically constructed oscillating systems,such as oscillating chambers, coaxial resonance lines, etc. Particularlytheir use in the last-mentioned field, the requirements on the condenserare particularly high, especially concerning its loss tangent, since onone hand the loss capacity increases proportional with the operatingfrequency, while on the other hand at these high frequencies therequirements concerning the resonance sharpness and therewith thecircuit quality are frequently particularly high.

In order to fulfill these requirements, particularly With respect to asmall loss tangent, it was heretofore believed that the deciding factorfor this requirement resided in the loss producing property of thedielectric used in the condenser.

It was, however, discovered that also other factors influence the lossesconsiderably, and it is an object of the invention to reduce theselosses still more independently of the material which is used asdielectric.

In accordance with the invention, the tubular condenser of variablecapacity comprises a tubular member provided with an exterior layer andpiston axially slidably mounted in the interior of said tubular memberand serving as an inner layer. The piston is axially adjusted by anaxially extending threaded spindle which latter forms a path for theelectric current to the piston, and this path is made shorter bychanging the profile of the thread on the spindle.

It was discovered that when applying this means of the invention thatthe total loss tangent tg 5 of the condenser, when it otherwise has thesame construction, is reduced from 15-10 to 1l-10 In the following, afew embodiments of condensers of the invention will now be described ingreater detail by way of example with reference to the accompanyingdrawing, in which:

FIG. 1 illustrates in a longitudinally axial section a tubular condenserof variable capacity;

FIGS. 2 and 3 illustrate each, partially in section, a differentthreaded spindle which may be used in the condenser of the presentinvention; and

FIG. 4 illustrates in cross-section still another example of a threadedspindle which may be used in the condenser of the present invention.

Referring to FIG. 1, the condenser comprises a tubular member 5 made ofa dielectric, such as glass, on one end of which is attached a mountingflange 1 provided With an exteriorly threaded mounting projection 1a andan interiorly threaded cylindrical projection 1b extending axially intothe tubular member 5. A threaded spindle 2 extends through the threadedprojection 1b and carries on its inner end a piston 3 which slidablyengages the inner wall of the tubular member 5 and forms the inner layeror electrode of the condenser. The other electrode of the condenser isformed by an exterior layer 4 fixedly attached to the outercircumference of the tubular member 5. Upon rotation of the threadedspindle 2, the piston 3 is axially adjusted within the tubular member 5relatively to the stationary outer layer 4.

According to FIG. 2, the thread of the spindle 2 has its crests removedto form a flattened helical perimeter 2a so as to make the threadprofile trapezoidal, while according to FIG. 3 the root of the thread 2bon the spindle 201 is formed by flattened valleys 2e. In both theseembodiments, the selected shape of the profile of the thread reducesconsiderably the path for the electric current between the fiange 1 andthe piston 3.

In the embodiment of the invention illustrated in FIG. 4, the threadedspindle 2c is provided with three circumferentially lengthwise oraxially extending grooves 2h which have a radial depth extending down tothe root diameter of the thread.

What I claim is:

1. A tubular condenser of variable capacity comprising a dielectric inthe form of a tubular member, an exterior electrode fixedly mounted onthe outer circumference of said tubular member, a slidably mounted innerelectrode within said tubular member, said slidable electrode comprisinga piston axially slidably arranged in said tubular member and attachedto an axially extending threaded spindle threadedly supported in amounting flange at one end of said tubular member, the thread on saidthreaded spindle having flattened crests to have a trapezoidal profilewhich reduces at high frequencies the supply conductor resistance forthe electric current passing from the spindle to the piston by reducingthe length of the current path.

2. A condenser according to claim 1, in which the root portion of thethread on the threaded spindle is flattened.

3. A condenser according to claim 1, in which the thread on the threadedspindle is provided with a plurality of lengthwise extending grooves.

References Cited UNITED STATES PATENTS 2,922,093 1/1960 Kellerman317-249 LEWIS H. MYERS, Primary Examiner.

E. GOLDBERG, Assistant Examiner.

1.A TUBULAR CONDENSER OF VARIABLE CAPACITY COMPRISING A DIELECTRIC INTHE FORM OF A TUBULAR MEMBER, AN EXTERIOR ELECTRODE FIXEDLY MOUNTED ONTHE OUTER CIRCUMFERENCE OF SAID TUBULAR MEMBER, A SLIDABLY MOUNTED INNERELECTRODE WITHIN SAID TUBULAR MEMBER, SAID SLIDABLE ELECTRODE COMPRISINGA PISTON AXIALLY SLIDABLY ARRANGED IN SAID TUBULAR MEMBER AND ATTACHEDTO AN AXIALLY EXTENDING THREADED SPINDLE THREADEDLY SUPPORTED IN AMOUNTING FLANGE AT ONE END OF SAID TUBULAR MEMBER, THE THREAD ON SAIDTHREADED SPINDLE HAVING FLATTENED CRESTS TO HAVE A TRAPEZOIDAL PROFILEWHICH REDUCES AT HIGH FREQUENCIES THE SUPPLY CONDUC-